The objects of evolved universal terrestrial radio access (E-UTRA) and universal terrestrial radio access network (E-UTRAN) are developing a radio access network towards a high data rate, low latency, packet optimized system with improved system capacity and coverage. In order to achieve these objects, an evolution of the radio interface as well as the radio network architecture is being considered. For example, instead of using code division multiple access (CDMA) which is currently used in third generation partnership project (3GPP), orthogonal frequency division multiple access (OFDMA) and frequency division multiple access (FDMA) are proposed air interface technologies to be used in the downlink and uplink transmissions, respectively. One big change is to apply all packet switched service in long term evolution (LTE), which means all the voice calls will be transferred on the packet switched basis.
3GPP Release 6 defined multimedia broadcast multicast services (MBMS). It is a counterpart of other multicast services operating in other spectrum, such as digital video broadcasting-handheld (DVB-H). MBMS allows downlink data to be transmitted from a single source to multiple recipients in broadcast or multicast modes. The 3GPP release also defined the MBMS channels, scheduling, bearers, procedures, etc.
In the 3GPP LTE project, a new E-UTRAN and evolved core network are introduced. This requires the changes to the current specifications for MBMS so that the new architecture can support MBMS service efficiently.
Two MBMS transmission modes are defined in E-UTRA/E-UTRAN: multi cell transmission and single cell transmission. Multi cell transmission uses single frequency network (SFN) operation to improve the cell edge performance by combining MBMS signals from other cells. An SFN is a broadcast network where several transmitters simultaneously send the same signal over the same frequency channel. The SFN operation needs additional synchronization mechanism and much more transmitting power on an MBMS traffic channel (MTCH) to cover the cell edge.
Single cell transmission transmits as a unicast service for some special service requirement and less user instance. Single cell transmission may use technologies, such as hybrid automatic repeat request (HARQ), multiple-input multiple-output (MIMO) or the like to improve the quality of service (QoS) of the MBMS service to specific users.
For the single cell transmission, there are two different transmission schemes: single cell point to multi-point (SC-PTM) and single cell point to point (SC-PTP). The single cell transmission scheme is determined based on the actual user distribution status.
The transmission mode/scheme is a part of radio configuration parameters for an evolved MBMS (E-MBMS) service. The transmission mode selection is made by an MBMS control entity (MCE). The single cell transmission scheme is determined by an evolved Node-B.
Network and resource optimization for MBMS service is made based on statistics that reflects the performance of the air interface. The statistics is collected regularly from a user equipment (UE). The statistics is collected from the layers of the radio protocol stack which maintains counters, (e.g., counters for detected procedures, successful and unsuccessful procedures, successful and unsuccessful reception of data, etc). It is common that such counters are maintained according to geographical information, (e.g., per cell). Such statistics may be used for continuous network performance monitoring and to verify that the network is operating correctly and efficiently.
Since large part of MBMS services will be transmitted via an SFN (multicast broadcast SFN (MBSFN)), configuring the SFN area is important. Static operation and maintenance (O&M) SFN configuration and dynamic SFN configuration (standardized) have been considered.
The static O&M SFN configuration limits the flexibility for MBMS services (especially for subscription based services). In case of static O&M configured SFN, a lot of resources (both radio and transport) would be wasted since MBMS content is always transmitted within the full SFN coverage area (most likely the MBMS service area), regardless of the distribution of users in the network. This is illustrated in FIG. 1. Small dots represent UEs. The SFN areas from a coverage planning point of view need to be over dimensioned in order to compensate for lacking the knowledge of where interested users are located. The static O&M configured SFN may suffice for services that are localized to a specific small area, but lacks the flexibility to adjust with respect to the actual load and usage from MBMS user population and location.
Dynamic configuration of SFN area based on user demand and changes of user distribution have been proposed. This dynamic SFN configuration is illustrated in FIGS. 2A and 2B. As the user distribution changes (small dots represent UEs), the SFN area is also adjusted from FIG. 2A to FIG. 2B. Dynamic SFN configuration may lead to more efficient usage of resources because it allows creation of an SFN for the duration of specific services, and local resource is optimized in a cell, (switching from multi cell transmission (i.e., SFN) to single cell transmission, or vice versa). An MCE dynamically creates an SFN area based on certain input. The MCE may also modify the SFN area throughout the service duration given the input, such as user joining or leaving the services of the SFN area.
Dynamic SFN area configuration based on tracking area (TA) update is slow to adapt to UE mobility. Expanding the SFN area based on TA may lead to adding more cells/eNode-Bs than necessary to the current SFN area, which will waste resources. Dynamic SFN area configuration based on cell update is too dynamic so that it may cause more system complexity and may ignore the SFN gain for UEs if only one cell is added each time. Making SFN area expansion and shrinking decision based on the criteria such as UE numbers may lead to degradation of other UEs MBMS reception performance, or too often activation and deactivation of MBMS service for certain eNode-Bs, which cause extra system complexity.
In the single cell MBMS transmission mode, specific MBMS on/off operation is dependent on whether there are UEs interested in specific MBMS service. In 3GPP release 6/7 MBMS, a counting procedure is used to obtain the number of interested UEs within one mixed cell for specific MBMS service. The MBMS on/off decision and PTP/PTM switch decision are made based on the counting results by the radio resource management (RRM) entity.
The problem of using counting procedure is that the network is not aware of UE situation. In addition, if counting is used more frequently it will cause signaling overhead, and if counting is used less frequently it may delay the MBMS on/off operation and PTP/PTM switch. This is a big issue when unicast traffic load is heavy within a cell. For example, if no UE is interested in specific MBMS service but at the same time there is heavy demand for downlink unicast services from other UEs, waiting for counting result to make resource re-allocation decision for MBMS service will cause resource waste.
In LTE, the resource may be dynamically allocated. This requires more efficient and flexible resource allocation strategy when MBMS and unicast services are supported together within one cell, (i.e., mixed cell). For example, when a UE is out-of-sync and cannot receive the MBMS service correctly for a while, it will be a waste of resource if MBMS service is still delivered while there are more unicast service requests.
It has been proposed to allocate different MBMS services with different MBMS priorities to a dedicated carrier and a mixed cell separately. For example, a long term MBMS service, (such as TV broadcast), may be transmitted through an MBMS dedicated cell and a short term MBMS service, (such as short messages), may be transmitted via a mixed cell. However, there is problem if one or more UEs want to listen to different MBMS services simultaneously.